Effects of dexmedetomidine on the minimum alveolar concentration and its derivatives in sevoflurane-anesthetized cats

To evaluate the effects of dexmedetomidine on the sevoflurane minimum alveolar concentration (SEV_MAC), minimum alveolar concentration (MAC) for blocking adrenergic responses (SEV_MAC-BAR), and MAC for tracheal extubation (SEV_{MAC-Extubation}).

Prospective randomized, crossover experimental study.

Six healthy adult neutered cats [one female and five males; weighing 4.8 ± 1.1 kg (mean ± standard deviation)].

Cats were anesthetized with sevoflurane in oxygen. After endotracheal intubation, anesthesia was maintained with sevoflurane and mechanical ventilation was performed. Each cat was given all six treatments in a random order, which were saline or dexmedetomidine infusions at maintenance doses of 0.15, 0.3, 0.6, 1.5, or 6.0 μg kg^-1 hour^-1, following respective loading doses of 1, 2, 4, 10, and 40 μg kg^-1 over 20 minutes, designed to achieve an estimated plasma concentration of 0.5-20.0 ng mL^-1. SEV_MAC-BAR, SEV_MAC and SEV_{MAC-Extubation} were measured in this order. Plasma dexmedetomidine concentrations were determined using liquid chromatography-tandem mass spectrometry. A linear regression analysis was used to assess the plasma concentration-response relationships and estimate the half-maximal inhibitory concentration (IC₅₀), defined as the plasma dexmedetomidine concentration producing a 50% reduction from the control value, separately for SEV_MAC-BAR, SEV_MAC, and SEV_{MAC-Extubation}.

The baseline SEV_MAC-BAR, SEV_MAC and SEV_{MAC-Extubation} were 2.79 ± 0.86%, 2.65 ± 0.32%, and 1.60 ± 0.64%, respectively. These values significantly decreased in a plasma dexmedetomidine concentration-dependent manner. The IC₅₀ values for SEV_MAC-BAR, SEV_MAC and SEV_{MAC-Extubation} were 1.90 ng mL^-1 [95% confidence interval (CI): 0.51-6.99 ng mL^-1], 1.38 ng mL^-1 (95% CI: 0.35-5.39 ng mL^-1), and 2.24 ng mL^-1 (95% CI: 0.67-7.50 ng mL^-1), respectively.

Dexmedetomidine reduced the MAC and MAC derivatives in a plasma dexmedetomidine concentration-dependent manner in sevoflurane-anesthetized cats.

Dexmedetomidine could be effective in suppressing motor and sympathetic responses accompanied by noxious stimulation and maintaining endotracheal intubation in cats.